Internal Microphone Not Detected by Pulse Audio / PulseAudio Volume Control

I have a Lenovo X1 Carbon 7th Generation running Ubuntu 18.04.2 LTS.

I am unable to use the internal microphone, as the device does not appear to be detected at all by the system settings:

system

In pavucontrol, under the “Input Devices” tab I have “Port: Microphone (Unplugged)” as well as “Monitor of Built-in Audio Analog Stereo” with some random static, but no sound signal is actually being picked up (using for example arecord or any other audio recording software).

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In the “Configuration” tab of pavucontrol, I’m using “Analog Stereo Duplex”, and have tried many other variants with no success.

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Other things I’ve tried without success:

  1. Editing /usr/share/pulseaudio/alsa-mixer/paths/analog-output-speaker.conf, as described in this Launchpad Issue. This patch makes the “Internal Microphone” show up in the System Settings, but there is still no audio being detected.

  2. Editing /etc/modprob.d/alsa-base.conf using various different options, as described here, here, and here. Maybe someone has a line that worked for them?

  3. Setting the right channel to silence in pavucontrol, as described here.

  4. Muting/unmuting the Microphone (which is “Capture”) via alsamixer.

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  1. aplay -L output is here .
  2. pactl list sources output is here.
  3. /proc/asound/cards output is:
~% cat /proc/asound/cards   0 [PCH            ]: HDA-Intel - HDA Intel PCH                       HDA Intel PCH at 0xea23c000 irq 167 

Microphone devices connected via the headphone jack or USB ports work fine, it is only the internal one that is not being picked up. Any help or ideas on getting the internal microphone to work would be greatly appreciated. Thanks.